In many people who are profoundly deaf, the reason for deafness is absence of, or destruction of, the hair cells in the cochlea which transduce acoustic data signals into nerve impulses. These people are thus unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to or absence of the mechanism for nerve impulses to be generated from sound in the normal manner.
It is for this purpose that cochlear implant systems have been developed. Such systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. U.S. Pat. No. 4,532,930, the contents of which are incorporated herein by reference, provides a description of one type of traditional cochlear implant system.
Typically, cochlear implant systems have consisted of essentially two components, an external component commonly referred to as a processor unit and an internal implanted component commonly referred to as a stimulator/receiver unit. Traditionally, both of these components have cooperated together to provide the sound sensation to an implantee.
The external component has traditionally consisted of a microphone for detecting sounds, such as speech and environmental sounds, a speech processor that converts the detected sounds, particularly speech, into a coded signal, a power source such as a battery, and an external transmitter coil.
The coded signal output by the speech processor is transmitted transcutaneously to the implanted stimulator/receiver unit situated within a recess of the temporal bone of the implanted. This transcutaneous transmission occurs via the external transmitter coil which is positioned to communicate with an implanted receiver coil provided with the stimulator/receiver unit. This communication serves two essential purposes, firstly to transcutaneously transmit the coded sound signal and secondly to provide power to the implanted stimulator/receiver unit. Conventionally, this link has been in the form of a radio frequency (RF) link but other such links have been proposed and implemented with varying degrees of success.
The implanted stimulator/receiver unit traditionally includes a receiver coil that receives the coded signal and power from the external processor component, and a stimulator that processes the coded signal and outputs a stimulation signal to an intracochlea electrode assembly which applies the electrical stimulation directly to the auditory nerve producing a hearing sensation corresponding to the original detected sound.
Traditionally, the external componentry has been carried on the body of the implantee, such as in a pocket of the implantee's clothing, a belt pouch or in a harness, while the microphone has been mounted on a clip mounted behind the ear or on the lapel of the implantee.
More recently, due in the main to improvements in technology, the physical dimensions of the speech processor have been able to be reduced allowing for the external componentry to be housed in a small unit capable of being worn behind the ear of the implantee. This unit allows the microphone, power unit and the speech processor to be housed in a single unit capable of being more discretely worn behind the ear, with the external transmitter coil still positioned on the side of the implantee's head to allow for the transmission of the coded sound signal from the speech processor and power to the implanted stimulator unit. The availability of such behind-the-ear (BTE) units has provided a great benefit to cochlear implant system recipients and provided them with a new found freedom. This has been due in the main to there no longer being a need to carry a large unit around with them and the associated long cables to connect the body worn device to the microphone and the transmitter coil positioned on the side of their head.
While the dimensions of behind-the-ear units have reduced significantly from those worn on the body, the units are typically still larger than most conventional hearing aids due in the main to the space requirements for the speech processor and batteries within this unit as well as the intrinsic differences between hearing aids and cochlear implant devices. As behind-the-ear units need to satisfy the power requirements of the implant, a large proportion of the size of conventional behind-the-ear devices has been associated with housing the power source (batteries) to provide such power requirements. As the power requirements of implant recipients vary depending upon the coding strategies that are employed and the skin flap thickness of the recipient across which the power needs to be transmitted, a main design limitation of conventional behind-the-ear devices has resided in housing a sufficient power supply to cater for all recipient types.
While continuing improvements in microprocessor and battery design should lead to further miniaturisation of behind-the-ear units, perhaps to the extent that the unit could be worn within the ear, implantee expectations as to the level of performance and features of cochlear implant are also expected to increase. In order to meet this implantee-expectation, it is anticipated that there would need to be an unacceptably large increase in the size of presently known behind the ear units so negating any efforts to further miniaturise such units in the future.
Further to this, in most cases of cochlear implantation, the implant has only been implanted in one of the patient's cochleas, with the decision upon which ear the implantation is to occur being the result of extensive pre-operative consideration. Due to the design requirements of the conventional system, the cochlear implant system user finds that if they desire to wear a behind-the-ear processor, then in most cases they will wear it on the ear that has been implanted in order to reduce the amount of connecting leads required. It has been accepted that in the majority of cases when the patient has been implanted in only one ear, that for simplicity of use, the behind-the-ear unit has been won on the ear which has been implanted and only in special circumstances would this practice be altered.
The present invention therefore aims to provide a cochlear implant system which is capable of allowing more functionality to be incorporated in behind-the-ear units without increasing the sizes of such units and compromising the benefits which such systems provide to implant recipients.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.